This invention relates to pumping systems for service stations which dispense fuel such as gasoline into automotive fuel tanks.
Gasoline service stations normally include a number of fuel dispensers and storage tanks for the fuels. A pump-motor assembly is mounted in each tank and it pumps the fuel to a number of dispensers. Such a pumping system normally also includes controls such as a leak detector (either mechanical or electronic) and fault detectors. The pump-motor assembly is a fixed speed type which is turned on when fuel is to be dispensed, in the absence of a leak or other fault condition.
Automatic leak detectors have come into common use. In recent years vapor recovery systems have also come into use in some areas and, in fact, in some areas they have been mandated. Vapor recovery systems (Stage II) are designed to capture fuel vapor leaving an automotive fuel tank during filling and to conduct the vapor to the fuel storage tank or tanks.
As mentioned above, the prior art pumping systems include a fixed speed pump-motor assembly which is either on or off, and such an arrangement has a number of disadvantages. Each pump-motor assembly supplies fuel to a number of dispensers, and the fuel pressure varies with the number of dispensers in use at a given time. If only one dispenser is in use (nozzle open), the fuel pressure in the supply line typically is about 30-32 psi (pounds per square inch) and the nozzle delivers about 10-14 gpm (gallons per minute). If two dispensers are in use, the pressure at both nozzles drops to about 25-28 psi and the flow from each nozzle is about 8-10 gpm. The pressure and the flow rate drop further as additional nozzles are opened. If the pressure is at the high end of the range during fueling, there may be problems with splash-back and hydraulic hammering. On the other hand, if the pressure is at the low end, the time needed to fill a tank may be excessive.
Further, vapor recovery systems are most efficient when the fuel flow rate is at an intermediate value, and the current dispenser manufacturers state that the flow rate should be between 8-10 gpm. Further, the EPA regulations effective January, 1996 and January, 1998 state that the flow rate is to be less than 10 gpm when dispensing. A high pump pressure and pressure regulator valves could be used to meet this requirement, but pumping systems are different and may require customized equipment and/or adjustments.
Still further, leak detectors are most efficient when the pressure is relatively high, but as pointed out above, a high fuel pressure can produce other problems.
It is therefore an object of the present invention to avoid the foregoing disadvantages by providing an improved pumping system including a variable speed pump-motor assembly and controls therefor.